Subsidy on fruit and vegetables also needed, say researchers.
About 2400 lives a year could be saved by putting a 20 per cent tax on our saltiest, fattiest foods and by cutting the price of fruit and vegetables with a 20 per cent subsidy.
The system of penalties and rewards would swing purchasing towards healthier options, gradually leading to a healthier population, say researchers from the universities of Auckland, Otago and Oxford, who estimated the likely effects on New Zealand death rates.
Based on Statistics NZ data, they modelled the effects of a 20 per cent price increase or decrease of quantities purchased and subsequent death rates from heart attack, stroke, diabetes and diet-related cancers.
The biggest effect of an individual component - a 6.8 per cent reduction in overall mortality - was from a 20 per cent price bump in food groups that are important contributors to our salt intake. These include bread and breakfast cereals; processed meat; sauces and condiments; beef, lamb hogget and poultry; and takeaway food and drink.
This was followed by a 5 per cent mortality reduction from a 20 per cent hike in price of food groups that contributed at least 5 per cent to saturated fat intakes.
Slicing 20 per cent off fruit and vegetables made death rates dip 1.9 per cent but when added to the salt and fat taxes, the life-saving power swelled to 8.1 per cent.
A 20 per cent tax on the major food groups that contribute to greenhouse gas emissions produced a 4 per cent mortality reduction.
A sugar tax was not modelled because the data relating price and purchasing changes was considered unsound.
Due to there being crossover items in the food categories, the total number of lives saved was lower than if all the categories had simply been added together.
Lives saved from a greenhouse gas tax were not included in the 2400 total.
If the taxes and incentives were applied, a 150g pack of potato chips would rise from about $2 to $2.40 and a steak and cheese pie would climb from $3.00 to $3.60.
Bananas would fall from about $3.00 a kilo to $2.40 and tomatoes would drop from $9.00 a kilo to $7.20.
The study, published today in the journal PLOS ONE, also predicted several perverse outcomes.
"The sodium [salt] tax would reduce sodium but would also result in a small increase in saturated fat purchases and a small decrease in vegetable purchases," said one of the authors, Professor Cliona Ni Murchu, of Auckland University, "but there was still a net benefit."
They studied food groups because this was the data most readily available but this lumped healthier options, such as low-fat milk, in with full-fat versions.
But if the Government adopted the study's tax-and-subsidy scheme, Professor Ni Murchu said it would need to discriminate between healthy and unhealthy products within a group.
"If you are serious about tackling obesity and unhealthy diets it is clear that price is a good lever for change," she said.
A spokeswoman for Health Minister Jonathan Coleman, whose Government has repeatedly ruled out fat and sugar taxes, said he would not comment until the "work programme in this area" was complete.
Food and Grocery Council chief executive Katherine Rich said computer modelling was far from the complexities of people's purchasing decisions and supermarkets' pricing and promotions strategies.
"I don't think using the New Zealand tax system to subsidise brussels sprouts by 20 per cent will make people eat more of them, or any vegetable for that matter."